Groundwater Resources, Development and Managementin the Kanto Plain, Japan
Tadashi Tanaka
Graduate School of Life and Environmental Sciences, University of Tsukuba,Ibaraki 305-8572, Japantadashi@atm.geo.tsukuba.ac.jp
Abstract
This report describes briefly the outline of groundwater resources, development andmanagement in the Kanto Plain, Japan, where the successful regulation forgroundwater extraction and the relatively high groundwater recharge rates due toJapan’s humid and temperate hydrologic conditions have resulted in more sustainablewater usage at the present time. Environmental consequences according to theexcessive groundwater development and strategies for groundwater resource
management are discussed based on the Japanese experiences.
Introduction
The Kanto Plain is the largest coastal plain in Japan as shown in Fig.1. The plain isunderlain by Pliocene and Pleistocene sediments of the Kanto Tectonic Basin,
consisting of unconsolidated layers of silt, sand and gravel extend to a depth of morethan 3,000 m. Figure 2 shows the east-west geologic cross section across the Tokyo
Metropolitan area to a depth of around 500 m below the sea level. These sediments
form the main confined groundwater aquifers.

TochigiGunma

Ibaraki

Saitama
MuTokyoChibaFig. 1 Topographic map of the Kanto Plain (Endo, 1992)

Fig. 2 East-west geologic cross section across the Tokyo
Metropolitan area (Endo, 1992).

The area for groundwater development in the Kanto Plain is about 13,300 km2 andestimated total storage volume of groundwater resources reaches 5,000 x 108 m3.
These confined groundwater resources have been mainly exploited for householdwater supplies and industrial, air-conditioning uses and irrigation and drainage in theKanto region for nearly eight decades. Total amounts of groundwater use in the Kanto
Plain in 1999 were estimated as about 12 x 108 m3/year. Heavy utilization of confinedgroundwater in the past decades, especially the period of high economic growth inJapan of 1960’s, serious problems related groundwater development such as land
subsidence, groundwater salinization, oxygen-deficient air accident have appeared
over the alluvial low lands and a part of terraces within the plain. Figure 3 shows theJapanese experience of environmental consequences according to the excessive
groundwater development.
Excessive groundwater development
Lowering of piezometric headLand subsidence

Zero-meter
zone

Difficulties ingroundwater use

Protrusion ofwell casing etc.

Groundwatersalinization
Oxygendeficient airFig.

3Japanese

Damages by floodand high tide

Damages of road,
public utilities etc.
Damages bynegative friction

experienceofenvironmental

consequences according to the excessive groundwater
development (Kayane, 1989).

Figure 4 shows the cumulative land subsidence at main benchmarks in the Tokyo
area. Land subsidence has resumed in the middle of the 1950’s when industries began
pumping up large quantities of groundwater to support increased production activity.
The cumulative land subsidence at the benchmark of No.9832 amounted to over 4.5 m
from 1918 to 2000. Land subsidence in Tokyo has been rapidly reduced since about
1973 due to the restrictions for extraction of groundwater by means of the laws and theordinance mentioned below.

Ita(7)Ko(6)Kita(14)

(473)
Ko(6)

(3365)

Cumulative land subsidence (m)Ki(2)

Kita(18)

No.

Cum. subsid. (m)From9832-4.5144

19183377-4.2925

1892

Mu(5)

-3.4269

1935

9836

-2.3655

1918

Ko(6)

-1.0577

1935

3365

-1.49701892

Kita(14)-1.6061

1958

Kita(18)-1.25621958

Ita(7)- 1.2033

1958

473

- 0.8357

1933

Ki(2)

- 0.6492

1973(9836)

Mu(5)(3377)(9832)

Fig. 4 Cumulative land subsidence at main benchmarks in
the Tokyo Metropolitan area (Imai, 2002).

Because of the serious problems related to the excessive groundwater use, theNational Government has restricted extraction of groundwater for industrial use by theIndustrial Water Law since 1961, and for air-conditioning use by the Law on
Regulating the Extraction of Groundwater for Use in Buildings since 1963. The areas
regulated by the laws are surround Tokyo Bay, the eastern part of the TokyoMetropolis, the southern part of Saitama Prefecture, and the western part of Chiba
Prefecture. In addition, local governments such as Tokyo’s and each prefecture within
the plain have also restricted the drilling of new wells in the area not covered by thenational laws applying the each prefecture’s ordinance. By the recognition of the local
governments that these control regulations are highly effective, the area subjected theimplementation has been gradually increased.

Changes of piezometric heads of confined aquifers due to the groundwater
development in the Kanto Plain
Figure 5 shows changes of the piezometric heads of confined aquifers in the Tokyo
area from 1954 to 1999. History of groundwater development in the Kanto Plain istypically shown in this figure. Water demand in the Tokyo and its surrounds had
increased after the World War II. The extra demand was fueled by Japan’s higheconomic growth resulting in over-extraction of the groundwater resource. In the early
1970’s, piezometric heads in several observation wells had declined to more than 40 m
below the ground surface.
1955

1960

1965

1970

1975

1980

1985

1990

1995

1999

Piezometric head (m)

K1

Ku1
Ne2
Ita･To1
Shin
Ko3

Kou･Ka1

Screen depth
SuA1
ShinadaShine2

Fig. 5 Changes of piezometric heads of confined aquifers in the Tokyo
Metropolitan area (Kawashima, 2001).

Fig. 6 Groundwater potential distributionof the confined aquifer in the Kanto Plainin 1975 (Prefectures Governor’s Association of the Kanto Region, 1991).

The groundwater potential distribution of the confined aquifer in the Kanto Plain in1975 is shown in Fig. 6. This figure clearly shows that the large declined piezometricheads centered surround the Tokyo area in the year.
After implementing regulations mentioned above groundwater potentials haverecovered so quickly as shown in Fig. 5 for better than was expected. Annual
precipitation of the Kanto Plain is about 1,300 to 1,600 mm, while the potential
evapotranspiration is estimated as 700 to 800 mm/year. Therefore, the residual 500 to
900 mm/year of water can be expected as the potential recharge rate in this region.
These values correspond to the daily recharge rates of 1.4 to 2.5 mm. It is believed that
because of this high recharge rate, the piezometric heads of the confined aquifers haverecovered so quickly.
Countermeasures to prevent the land subsidence
Two groundwater laws are effective in whole Japan, but practical application of laws to
a specific area is decided by the local government. The Tokyo Metropolitan
Government has succeeded in reduce the rate of land subsidence by converting water
resources from groundwater to surface water and by making legislative guidance inorder to save groundwater resources in factories and buildings. However, bordering
prefectures such as Saitama, Chiba and Ibaraki in the same Kanto Plain are still
suffering from the land subsidence as shown in Fig. 7.
Tochigi

Kitakawabe obs. well
Gunma

Ibaraki
Nogi obs. well
Koga obs. wellMeiwanishi obs. well

Urawa 2 obs. well
Saitama

Tokyo
Chiba

Obs. area
Preserv. area

Cumulative land subsidence (mm)Fig. 7 Areal distribution of cumulative land subsidence in the Kanto
Plain during the 10-year period from 1988 to 1997 (Ministry of Land,Infrastructure and Transport, 2002).

This figure shows cumulative land subsidence during the 10-year period from 1988
to 1997 in the Kanto Plain. The center of the land subsidence in the period exists in thenorthern part of the plain. In 1950’s, the land subsidence in the Kanto Plain was most
severe in the southern part of Saitama Prefecture, and gradually spread over for areas
such as the northern part in Saitama Prefecture, the western part in Ibaraki Prefecture,
the north-western part in Chiba Prefecture and the southern part in both Gunma andTochigi Prefectures. In 1999, a total area of about 120 km2 subsided 1 cm or more/year
and of about 1 km2 subsided 2 cm or more/year in the northern part of the Kanto Plain.
The maximum land subsidence recorded in 1999 was 3.3 cm in the northern part of thearea.
According to the situation of the land subsidence in the northern part of the Kanto
Plain, the National Government has decided to formulate the Guideline for Measures
to Prevent Land Subsidence in the Northern Part of the Kanto Plain in November 1991.
The purpose of the Guideline is to prevent the land subsidence through comprehensive
promotion of policies related to prevent the land subsidence in that area. In theGuideline, the target extraction quantity of groundwater in the prevention area isformulated as 4.8 x 108 m3/year. The total extraction of groundwater in the area in1999 was 5.1 x 108m3/year, and exceeded the quantity than that of the target volume.
The target year of the present Guideline was set in the fiscal year of 2000. The
National Government has been setting up in the work to improve the contents of theGuideline.
Concluding remarks
This report showed a typical example of excessive extraction of groundwater resources
and their resulting problems suffered in the Kanto Plain, Japan. In the case of theKanto Plain, this problem has been remedied by the implementation of regulations
over past 30 years and the relatively high recharge rate due to the natural hydrologic
conditions of the area.
For sound groundwater management, the information on pumping amounts in timeand space, hydrologic parameters, aquifer characteristics, quantities of irrigation anddrainage and so on should be unified so as to make the groundwater resource
management effectively. Appropriate legislative and administrative measures are
essential for providing background for acting the proper groundwater management. It
requires the knowledge of hydrologic balance between the quantity of recharge rate
and the extraction of groundwater for the sustainable management of groundwater
resources. A balanced budget is the goal for all groundwater managers.
Furthermore, to maintain the continual social and economic growths of the area andto minimize the enlargement of the environmental problems related to the groundwater
development, it should establish the continuous monitoring systems such as
groundwater levels, quantities of extraction, and the land subsidence as well asmonitoring the groundwater pollution.
References
Endo, T. (1992): Confined groundwater system in Tokyo. Environ. Geol. Water Sci., 20,21-34.
Imai, T. (2002): New policy for groundwater preservation in Tokyo Metropolitan area.
Groundwater Technology, 44(3), 14-21. (in Japanese)
Kawashima, S. (2001): Groundwater environment in Tokyo. Groundwater Technology,43(3), 6-19. (in Japanese).
Kayane, I. (1989): Personal communication.
Ministry of Land, Infrastructure and Transport (2002): Evaluation of the Guideline for
Measures to Prevent Land Subsidence in the Northern Part of the Kanto Plain. 36p.
(in Japanese)
Prefectural Governor’s Association of the Kanto Region (1991): Research report of thedistribution of groundwater level in the Kanto groundwater basin. 65p. (inJapanese)